(a) Field of the Invention
The present invention relates to a semiconductor device comprising a metal-insulator-metal (MIM) capacitor having a high permittivity film for use in a microwave range, and a method for fabricating such a semiconductor device.
(b) Description of the Related Art
A MIM capacitor is known which comprises a high permittivity film, i.e., a thin film having a high dielectric constant, such as made of BaTiO.sub.3, SrTiO.sub.3, (Sr.sub.x,Ba.sub.1-x)TiO.sub.3, PbTiO.sub.3, Pb(Zr.sub.x,Ti.sub.1-x)O.sub.3 and SrBi.sub.2 Ti.sub.2- Nb.sub.x O.sub.9, and has an advantage of high capacitance per unit area. The MIM capacitor is generally used in a high density integrated circuit, such as a memory device, for use in a microwave range. Such a capacitor having a SrTiO.sub.3 film, for example, is reported in "IBM Journal of Research and Development", Nov. 1969, pp686-695. It is reported that, among others, sputtered SrTiO.sub.3 and (Sr.sub.x,Ba.sub.1-x) TiO.sub.3 films are especially useful because these films can be formed below 650.degree. C. which is the decomposition temperature of a GaAs substrate.
A conventional process for manufacturing a semiconductor device having a MIM capacitor and a FET or active element generally comprises the step of forming a FET or active element after the step of forming the MIM capacitor having a bottom electrode, a capacitor insulator film and a top electrode. In some cases, an additional process film, such as an insulator film, for forming thereon interconnections may be formed before forming the FET or bipolar transistor. The through-holes for the top and bottom electrodes are generally formed by a single step using a mixed gas of CHF.sub.3 and H.sub.2. To obtain perfect through-holes, over-etching by 100% is generally used wherein the etching time is double the normal time length considered to be sufficient for etching through-hole for exposing the bottom electrode.
In a conventional semiconductor device having such a MIM capacitor, contamination in the transistor (FET) regions is sometimes observed due to the impurity elements and alkaline-earth metals which ate eluded from the high permittivity film during pretreatment of substrate surface by using a hydrochloric acid solution before formation of the process film, resulting in degradation of FET characteristics.
In addition, a high substrate temperature during formation of a high permittivity film causes leakage current in substrate, which retards the sufficient insulation between the active elements. Moreover, the bottom electrode disposed in contact with the substrate defines the configuration of the circuit including the capacitor to thereby limit the design choice of the circuit. Further, the 100% over-etching for the bottom electrode causes 200-400% over-etching for the top electrode, which damages the high-permittivity film and the top electrode due to the ion damage or reducing gas, resulting in a higher leakage current in the MIM capacitor.